AA.H3L3 Baltic photic muddy sediment dominated by ocean quahog (Arctica islandica)


HELCOM RED LIST Biotope Expert Team

Textual description            

Baltic photic zone bottoms with at least 90 % coverage of muddy sediment. The sediment must contain at least 20 % of mud, silt or clay (grain size less than 63 ┬Ám). Biomass of infaunal bivalves dominates and is highest in the group that includes infaunal bivalves/polychaetes/crustaceans/echinoderms/insect larvae. Out of the infaunal bivalves ocean quahog (Arctica islandica) constitutes at least 50 % of the biomass.

Physical environment       

Substrate is muddy sediment. Appears in low to moderate energy exposure classes.

Characteristic species        

Arctica islandica

Quality descriptors             

Diversity, abundance and biomass of fauna.

Geographic range               

Western Baltic Sea

Anthropogenic threats     


Correspondence with other classification systems               

HELCOM 1998:

2.7 Muddy bottoms

2.7.2 Sublittoral photic zone With little or no macrophyte vegetation

EUNIS 2012:

A5 Sublittoral sediment

A5.3 Sublittoral mud

A5.31 Sublittoral mud in low or reduced salinity

A5.311 Baltic brackish water sublittoral muddy biocenoses influenced by varying salinity


 Related information

This biotope has been listed as Near Threatened (NT) in the HELCOM Red List of Baltic Sea biotopes and habitats.

See the Biotope Information Sheet of AA.H3L3